The present invention relates to a sprocket assembly which, when mounted on a film projector or other film handling device, permits the ready conversion of the device to run either 4-perf or 3-perf film, as the occasion requires.
Conventional 35 mm film projectors and cameras pull down four-perf film. "Four-perf" film signifies that each frame has four perforations along the two side edges of the film. The perforations are all spaced apart the same distance, known as the pitch length. The "pulldown" operation in either production or projection of films involves engaging the perforations on the sides of each frame with a claw gear and bringing the frames, in sequence, into register with the appropriate apertures for exposure or projection. Four-perf pulldown means simply that to place each frame in front of the appropriate aperture at the proper time, the four perforations along the sides of each frame are engaged and pulled down together. Currently, longtime worldwide use and acceptance of four-perf pulldown has led to its being the standard format for both production and projection of films.
Historical accident is largely responsible for the advent and current widespread use of four-perf film. The standard film gauge of 35 mm was first introduced by Thomas Edison in 1891 for use in a peep show viewing apparatus developed by his assistant, W. K. L. Dickson. Edison also chose a four-perf, 4:3 ratio frame format, where the frame width to frame length ratio is 4:3, because it happened to be compatible with this particular peep show viewing apparatus. At that time, Edison gave no thought, apparently, to that format's ever being used in the projection of motion pictures. As it turned out, this 4:3, four-perf frame format was recognized as the world standard by 1907, after the Lumiere brothers of Lyon, France, builders of the first commercially successful projectors, followed Edison's lead by accepting that format for the European film industry.
In early films, the so-called "full aperture" frame format was used. The full aperture format had a 4:3 ratio of frame width to frame length (the length being measured along the longitudinal extent of the film), otherwise known as the 1.33 aspect ratio, and resulted in nearly the entire length of film being exposed or utilized, since there was very little unexposed film between frames. With the addition of sound during the 1920's, the image size on the film was reduced to allow room for the sound track to be printed adjacent to one row of perfs. In order to accommodate the sound track, the image size was reduced in both width and length, maintaining the 4:3 or 1.33 aspect ratio, so that a greater amount of unused or unexposed film was left between frames. The reduced size, 4:3 ratio frame format is known as the "academy aperture."
To achieve a wider projected image, and thus more closely resemble a theatrical stage, the 4:3 frame format was changed to accommodate projection on a flat, wide screen. In North America, the image size was reduced from the academy aperture and conformed into a 5.5:3 ratio, popularly known as the 1.85 aspect ratio. In Europe, the flat, wide screen frame format was conformed into a 1.66 aspect ratio, which again resulted in an image size smaller than that obtained with the academy aperture.
To achieve either the 1.85 or 1.66 wide, flat screen format in a theater from a 35 mm film, two techniques are presently employed: (i) a mask is placed in the projector gate, or (ii) a "hard matte" is used in the camera. In both cases, the 35 mm camera advances the film four perfs at a time, for each frame. The mask in the projector gate is employed when a camera is used for filming which is adapted to produce an image on the film having a 1.33 aspect ratio, since it is necessary to restrict the height of the 1.33 frame when projecting onto a screen requiring a 1.85 or 1.66 frame. The mask in the projector gate cuts off the unnecessary top and bottom portions of the 1.33 image so that it will fit the 1.85 or 1.66 image format. On the other hand, the "hard matte," which is also a type of mask, in the camera is used to record a photographic image which has the correct wide screen ratio. The mask in the camera results in a wide, unexposed portion of film between each frame and the adjacent frames.
With either of the above two techniques for obtaining the correct 1.85 or 1.66 aspect ratio image, the amount of film used is of the order of one-third greater than the combined length of the photographic images and the required spacing between images, assuming, again, that 4-perf pulldown is employed. In other words, about 25% of each film is presently not being used. This excess film results in unnecessary expense for buying, processing, editing, and printing of the film used for motion pictures, as well as extra expense for storage, shipping, handling, add the like.
Another wide-screen film technique known as Cinemascope was introduced in the early 1950's. Cinemascope achieved a 2.35 aspect ratio through the use of anamorphic lenses, which squeezed the image into the 4:3 academy aperture frame in production, and subsequently unsqueezed it in projection onto a wide, curved screen. Normally, a 4-perf pulldown 35 mm camera with a 2:1 anamorphic optical system would be used in filming. This system reduces the horizontal component of the scene which is recorded on the film. The projector uses a complementary 2:1 anamorphic optical system such that the horizontal component of the image is increased to conform the proportions of the projected image to those of the scene filmed. Presently, the flat, wide screen format is more popular and widely used than the anamorphic 2.35 format.
For the last fifteen years or so, there have been proposals in the film industry to convert from 4-perf production, which is now the industry standard, to 3-perf production in order to eliminate the 25% of each film which is wasted, as referred to above. In other words, if the perforation spacing or pitch length were to remain the same, which it must for all practical purposes, a film using 3-perf pulldown, which has only 3 perfs per frame, is precisely 25% shorter than it would be using 4-perf pulldown, which has 4 perfs per frame. One such proposal is found in Lente U.S. Pat. No. 3,865,738, issued Feb. 11, 1975. The Lente patent discloses means for producing 3-perf films for flat, wide screens or anamorphic, curved wide screens. With the recent advent of production equipment that easily converts from 4-perf to 3-perf, and with the introduction of new film stocks that will facilitate 3-perf editing, the remaining stumbling block to industry-wide conversion to 3-perf films is the inability to convert cinema projectors easily and inexpensively to accept 3-perf or 4-perf release prints.
Currently, worldwide standard projection systems use a relatively heavy feed sprocket and hold-back sprocket, a lighter-weight intermittent sprocket between the feed sprocket and hold-back sprocket, and constant-speed sprockets associated with the accompanying sound track. These sprockets are all sized and run at the appropriate speed in order to project 24 frames per second ("fps") with a 60-cycle power supply, or 25 frames per second with a 50-cycle power supply. At a 24 fps projection rate, with 4-perf films using the worldwide standard pitch length, precisely 90 feet of film are run per minute.
If 3-perf films were to be produced and made available to cinema houses, modifications would have to be made to the projectors in order to project those 3-perf films. The object with 3-perf projection would still be to project at a rate of 24 fps, and since the sprocket shafts on the conventional projectors do not change their rates of rotation, changes in sprocket sizes would be necessary in order to effect the proper film running rate.
In order to project 24 fps of 3-perf film, precisely 67.5 feet of film would have to be run per minute. One way to effect the 67.5 feet-per-minute running rate required for 3-perf film projection would be to replace the sprockets used for 4-perf films with sprockets having only 75% of the diameter of the larger 4-perf sprockets, with the pitch length remaining the same. In one conventional projection system for 35 mm, 4-perf films, the 4-perf sprockets have 16 teeth around their circumferential peripheries on each end. Because the teeth on the projector sprockets must always have the same pitch length no matter whether 4-perf or 3-perf film is being projected, the 3-perf sprockets for this conventional system, being sized at 75% of the diameter (and, thus, the circumference as well) of the larger 4-perf sprockets, would have only 12 teeth around their circumferential peripheries at each end. Conversion of projectors involving removal of the 16-tooth sprockets (or any larger sprocket) and replacement with smaller 12-tooth sprockets (or any smaller sprocket), is a time-consuming, relatively expensive process, however, and after conversion to the smaller 3-perf sprockets the projection equipment could not be used to run 4-perf films. Conversion from 4-perf to 3-perf pulldown, and back again, depending on whether the film to be shown is 4-perf or 3-perf, is cumbersome, slow, expensive, and would simply not be feasible with existing equipment. See, e.g., "Study Group on 30 Frame Film Rate," International Photographer. December, 1988, at p. 20.
It can be seen that there is presently no incentive for making release prints for theatrical presentation in a 3-perf format; accordingly, release prints will still be made with 4-perf pulldown in order to be compatible with existing movie house projection equipment. This is so whether the production print of the film is in 4-perf or 3-perf format. As a result, the great cost savings which could be realized by making 3-perf release prints from 3-perf production prints, eliminating the 25% waste factor, will be lost as the 3-perf production prints are converted to 4-perf release prints, with their 75% image utilization, in order to be compatible with present movie house projection equipment. The savings which could be realized through making 3-perf release prints are due not only to the lower direct material costs, i.e., the lower cost of the film for the 25% shorter prints, but also to savings in printing or processing, storage, handling, shipping, and the like of such shorter, lighter weight films. Since many more release prints are made than production prints, the savings to be realized from making 3-perf release prints are potentially greater than those to be realized through simply making 3-perf production prints.
Another significant savings with use of 3-perf film is potentially available in conversion of film to video. Video is run at a scanning rate of 30 fields per second, not at the presently used film rate of 24 frames per second. Video which is produced from film must be specially processed to correct for these differences in rate. A desirable alternative to such special processing would appear to be to produce and project films at 30 fps. Production of videos from 30 fps films would not involve such special processing. Such an increase in film production and projection rates would, however, increase the amount of film used in a motion picture by 25%. With 3-perf film, even with an increase in production and projection rates to 30 fps to be compatible with video, film usage would still be less than with 4-perf film running at the standard 24 fps. Three-perf film running at 30 fps uses 84.375 feet of film per minute, compared with 90 feet per minute for 4-perf film running at 24 fps. These same relative film savings of about 6% will accrue whether one is using 3-perf film to produce standard video or High Definition TV. The latter is expected to become increasingly popular.
Thus, it will be appreciated that what is needed is a convenient, fast, simple, and inexpensive system for converting existing 4-perf projectors to make them readily compatible with and adaptable to either 3-perf or 4-perf prints. This will encourage production of 3-perf release prints, since theater operators will be able to show 3-perf in their theaters or 4-perf, as the case may be, without undue inconvenience, expense, or delay, thereby capturing the great cost savings referred to above and positioning the industry to still realize significant cost savings of the order of 6% in the event that a 30 fps film production and projection rate were to be adopted.